BEIJING (Reuters) - Ethnic Uighurs attacked police with knives and bombs at a traffic checkpoint in China’s far western Xinjiang region, Radio Free Asia reported on Wednesday, and at least 18 people were killed.

The attack occurred at the beginning of the Muslim fasting month of Ramadan on Monday in the southern city of Kashgar, where tensions between Muslim Uighurs that call the region home and the majority Han Chinese have led to bloodshed in recent years.

Hundreds have been killed in violence across the region, blamed by Beijing on Islamist militants.

Suspects killed several police officers with knives and bombs after speeding through a traffic checkpoint in a car in Kashgar’s Tahtakoruk district, U.S.-based Radio Free Asia said, citing Turghun Memet, an officer at a nearby police station.

Armed police responded to the attack and killed 15 suspects “designated as terrorists”, Radio Free Asia cited Memet as saying.

It said in all between 18 and 28 people were killed, including several bystanders, but that police estimates of the toll varied.

Repeated calls to the Xinjiang government and public security departments were not answered. Such incidents are frequently reported in overseas media but not confirmed by the Chinese government until days later, if ever.

Chinese Foreign Ministry spokesman Lu Kang told reporters that he could not immediately verify the report.

“But if it is correct, then the Chinese government has the responsibility to take resolute steps to stop these kinds of violent terror acts, to maintain peace and stability in Xinjiang,” Lu said.

The old Silk Road city of Kashgar is a frequent scene of unrest. Last year the government blamed Islamist militants for the murder of the imam of China’s biggest mosque.

Ramadan is a sensitive time. State media and Xinjiang government websites have published stories and official notices again this year demanding that Communist Party members, civil servants, students and teachers in particular do not observe Ramadan and do not fast.

Exiled Uighur groups and human rights activists say repressive government policies in Xinjiang, including controls on Islam and Uighur culture, have provoked unrest, a claim that Beijing denies.

Last week, a county in southern Xinjiang held a beer festival in what an exiled group called an open provocation, as Muslims are not supposed to drink alcohol.

China’s Communist Party says it protects freedom of religion. But it maintains a grip on religious activities and allows only officially recognized institutions to operate.

China has around 20 million Muslims, only a portion of whom are Uighur.